-Deficiency and Toxicity
Nitrogen (N)
Deficiency: Plants will exhibit lack of vigor as older leaves become yellow (chlorotic) from lack of chlorophyll. Chlorosis will eventually spread throughout the plant. Stems, petioles and lower leaf surfaces may turn purple.
Toxicity: Leaves are often dark green and in the early stages abundant with foliage. If excess is severe, leaves will dry and begin to fall off. Root system will remain under developed or deteriorate after time. Fruit and flower set will be inhibited or deformed.
Phosphorus (P)
Deficiency: Plants are stunted and older leaves often dark dull green in color. Stems and leafstalk may turn purple. Plant maturity is often delayed.
Toxicity: This condition is rare and usually buffered by pH limitations. Excess phosphorus can interfere with the availability of copper and zinc.
Potassium (K)
Deficiency: Older leaves are initially chlorotic but soon develop dark necrotic lesions (dead tissue). First apparent on the tips and margins of the leaves. Stem and branches may become weak and easily broken.
Toxicity: Usually not absorbed excessively by plants. Excess potassium can aggravate the uptake of magnesium, manganese, zinc and iron.